Adapting a bag to the Brompton frames (s) is easy if you’ve sewn before, and not too terrible if you aren’t an accomplished sewer. This DIY deals with the S-frame. I believe there are others out there, but since I own an S, I don’t have any experience with them. If this seems too complicated to you, there are TONS of people out there that make messenger bags, and could accommodate this pretty easily, if they do pure-custom stuff. If you’re dealing with a company that does custom colors but not designs, it may be harder. I do know that Swift and Guu Watanabe make bags using a similar frame set-up.
I have two bags set up for use with the frame now; a messenger bag and a backpack. I’m a huge proponent of messenger bags in general, but for this purpose I don’t really like the typical messenger bag I make – one designed to ride high on the shoulder. This is because I have to get the bag on and off several times on a typical commute (ride, fold, commuter train, fold, ride, fold, carry into the office). This is because the rack itself makes wearing a messenger bag across your body uncomfortable. With the backpack, it’s less noticeable, especially with the padding I added to mine (see above). But the frame itself makes most any bag stable, which is great.
So, I’m assuming you’ll start with a pre-made bag. Ideally, you take it apart, sew the frame pocket to the outer layer, then reassemble the bag. If what I said sounds confusing, or if you haven’t done it before, then it is probably best to just sew through your bag. If you are thinking about pulling apart your fancy messenger bag and don’t have much experience, I can almost guarantee you that it won’t look as good as it did. You can seam seal it later if you wish, though in practice I find that this won’t cause much if any ingress or water. But it is up to you and what you are comfortable exposing your stuff too.
½ yard of 1000D cordura
heavy grosgrain (milspec ,nylon, or polyester in order of preference)
1/3 or ¼ a yard of 2” velcro
This is the finished pattern, or I should say, this is where the stitches that attach the pocket to the bag go. The below image doesn’t have any edge allowances (at least 1/4 inch from where it is sewn for the finished bag), or allowances for fabric needed to finish the edges if you elect to not use grosgrain. So, the finished fabric piece would need to be at least 17.5 inches wide (.25 per side) and 11.25 high (.25 allowance at the top, none at the bottom, since it is not sewn down). The zig zagged lines are what is sewn to the bag itself:
The unintelligible version when I was laying it out on the fabric. Some marks are to make sure it is square, some are my 1/2 to 1 inch allowance:
I usually use 1000 denier Cordura for my sewing projects. It is stout and long wearing. Whatever you use, I recommend using some sort of heavy fabric. This isn’t a job for silnylon. I get most of my fabric from rockywoods.com. The quality is consistent and the prices are reasonable. You can also find fabric on eBay, but keep in mind that Cordura is manufactured under license, and quality can vary. And there are Cordura knock offs, which can be even more inconsistent. I wouldn’t doubt people selling the knock-off stuff on eBay as the real thing, since it is eBay. You wont need much, since for an S frame, we need a piece that is only 20 inches by 14 inches. Most places are going to make you order a yard. If you get lucky and find it locally, you might not have to, but the one place I’ve ever found it locally wants $20+a yard, making it cheaper to just get it online.
You’ll also most likely need some grosgrain ribbon and will need some thread. Nylon or mil-spec grosgrain is best, but a heavy polyester will work too. It is possible to make it without grosgrain. Nylon upholstery thread (Coates and Clark) is a thread you’ll be able to source most places, but a #69 nylon thread is ideal.
The Velcro is to keep the bag from possibly popping off when you hit a big bump. You don’t need much. You could get by with 6” of each side, though I do recommend using 2” and not narrower stuff.
I can think of two ways, broadly, to make it — with the grosgrain and without. Most of these pictures are on my backpack where I didn’t use grosgrain, but finished the edges by turning them over, sewing them down, then sewing them to a piece of vinyl coated polyester with a foam sandwich in between.
If you wanted to turn the edges over and sew them down, I think it would be OK, since the Cordura is a pretty stable fabric. But it will likely unravel a bit over time if you just fold it over once. If you get the untreated Cordura, it will CERTAINLY unravel, and quickly. The solution to this is to double fold it like this, so there is no raw edge:
The finished side to side dimensions (where the actual seam to the bag is) is 17 inches across on my messenger bag. This allows the frame to slide in and out, but isn’t overly loose. The backpack is 16.75 inches across, and is close to a press fit, which is good and bad. Good, in that there is little chance it can get out, but bad in that if it was any tighter, the frame wouldn’t fit. So, diagionally, using a ¼ inch seam allowance (how far the seam is from the edge), the fabric should be 17.5 inches across if you are using grosgrain, and 18.5 inches across if you aren’t. If you aren’t, plan on turning a half inch of fabric back to finish the edge (really folding a 1/4 inch over twice as in the pic above).
The finished vertical dimensions are 11 inches. I’ve made both of mine to expose the entire plastic piece of the frame, but you only have to have the portion that clicks in exposed. But if you cut it too close, it’ll be a pain to clip in and out if you have a piece of fabric that occasionally gets caught. The back piece is 5 inches wide at the bottom, four at the top of the piece, and is 3 1/2 inches tall. You also need to make sure you have a cut-out for the handle at the top. Otherwise, you won’t be able to use the handle as effectively. You could enclose the top entirely using a taller piece of fabric that I’ve shown here, but the handle makes it much easier to get the bag on and off the bracket. The inset on my messenger bag is just 1/2 inch. The backpack is a touch more than that.
If you use grosgrain, you can cut the lines straight and cut the grosgrain for each section, making sure to burn each end of the grosgrain with a lighter to seal it, but I highly recommend just making gentle curves and using one piece of grosgrain. If you turn the fabric back to finish it, you can just use straight lines and relieve each piece so it turns back flat.
Remember, I only turned the edge of this fabric once, since I was making a “sandwich” out of it. Turn yours over twice to hide the edge.
I think there are two ways to position the bag. The first is to align the bottom of the rack (that supports the bag in some small way, though not really) with the bottom of your bag. The second is the place your bag as low as possible, lowering the center of gravity. But you’ll run into the fender and tire before long. And even if you position the bottom of the rack at the bottom of your bag, you may run into problems. Both of my bags are positioned so that the bottom of the rack and bag are equal, but can still rub on the tire/fender when unloaded. Since both of these bags are deep front to back (6-8 inches) and don’t have any internal structure, if nothing is in them, they droop down.
See, no good.
Solving this isn’t a big problem – on my messenger bag I just have to make sure that I tuck the bottom of the bag under the front flap as much as possible. On the backpack, I’m using a strap around the middle to compress it. Any luggage strap will work. At some point I will add compression straps to this backpack. When loaded, both bags don’t have this problem, since they are both made to be quite rectangular when loaded.
Problem solved! And as you can see at the bottom, once loaded, there is no problem with my messenger bag.
How straightforward the sewing is depends on your bag and your machine. A pulled apart bag and an industrial machine is the best. A dinky home machine and a tough messenger bag (Re-Load, Chrome, Bailey Works, etc.) is the worst. If you want to add this to a quality messenger bag like those I’ve listed, and have a light home machine, I would probably do everything except sew the pocket and Velcro on to the bag (i.e. cut the piece, finish the edges using the method of your choice, sew a piece of hook velcro to the inside of the piece as explained below) then take it to an alternation shop, where they will have machines that can easily handle this. Also, if you want to sew through a bag, whatever rear pockets there are will be lost. Sorry.
But for actual sewing, there isn’t much to do. Cut the fabric, and either sew on the grosgrain, or turn the edges back. Ideally, the edges look something like this, turned back north/south, grosgrain east/west. Also trim your corners slightly so they dont stick out like on the top piece (over the yellow):
Sew a small piece of hook side Velcro to the bottom of the pocket facing the bag itself (or inside).
Sew a 2-3 inch length length of loop Velcro to the bottom of your bag one of two ways - with the loop side facing outward, and the loop Velcro sewn below the pocket. Here it is sewn below. Please note that the fabric looks distorted due to the curve at the bottom, and the grosgrain is pulling around the bottom cut out, since the curves are too sharp:
Or sew kind of the reverse of the above pic. Instead of having the patch on the bottom (where it gets dragged across stuff, and is hard to sew if you aren’t pulling the bag apart), sew the (hook type) patch on the inside of the bottom edge of the pocket, facing the body of the bag (down in this pic). Then sew a piece (2-3” long) of loop, also FACING THE BODY, but on the body itself, and in the same postion as the hook piece. The pieces won’t velcro to each other, unless you bend the loop piece in a U shape around the frame. This hides the velcro, more or less, under the pocket. Confusing? Here’s a picture:
MAKE SURE that only the loop side faces the outside, otherwise your clothes will get torn up. Remember that you are just making sure that the bag can’t slide up the frame. You could also use 1” buckles here, but I like velcro better.
Sew the pocket itself. The entire bottom is open, and the slot for the handle is open too. I sewed 4.5 inches on each side of the top on this one, leaving the middle open for the handle. In the drawing, the zig zagged lines are what is sewn to the bag itself.
I hope this is clear! If not, please let me know what isn’t and I’ll do my best to explain it. Feel free to ask me here, or on Twitter @codywms. Both of mine have worked well in action so far:
Touring on the GAP Trail:
Getting to work: